What is the correlation of in vivo wear and damage patterns with in vitro TDR motion response?

[cavalier]

What is the correlation of in vivo wear and damage patterns with in vitro TDR motion response?

You have to look at the link above for the full article but it is a interesting read - 1st I have seen of long term wear - this is on the Charite but it is important to read the entire article.

This is ALL based on lumbar folks - Jill
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Spine. 2008 March 1; 33(5): 481–489.

What is the correlation of in vivo wear and damage patterns with in vitro TDR motion response?

Steven M. Kurtz,1,2* Avinash Patwardhan,3 Daniel MacDonald,1 Lauren Ciccarelli,2 André van Ooij,4 Mark Lorenz,3 Michael Zindrick,3 Patrick O’Leary,3 Jorge Isaza,5 and Raymond Ross6
1 Implant Research Center, School of Biomedical Engineering, Science, and Health Systems and Department of Materials Engineering, Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104, USA. 2 Exponent, Inc., 3401 Market St., Suite 300, Philadelphia, PA, 19104, USA. 3 Loyola University Medical Center, Maywood, IL, USA. 4 Department of Orthopaedic Surgery, University Hospital Maastricht, 6202 AZ Maastricht, the Netherlands. 5 Baton Rouge Orthopaedic Clinic, 8080 Bluebonnet Blvd, Suite 1000, Baton Rouge, LA 70810. 6 Hope Hospital, Stott Lane, Salford, Manchester, M6 8HD, United Kingdom

Background Context
Total disc replacements (TDRs) have been used to reduce pain and preserve motion. However, the comparison of polyethylene wear following long-term implantation to those tested using an in vitro model had not yet been investigated.

Purpose
The purpose of this study was to correlate wear and damage patterns in retrieved TDRs with motion patterns observed in a clinically validated in vitro lumbar spine model. We also sought to determine whether one-sided wear and motion patterns were associated with greater in vivo wear.

Study Design
This two-part study combined the evaluation of retrieved total disc replacements with a biomechanical study using human lumbar spines.

Patient Sample
38 CHARITÉ lumbar artificial discs were retrieved from 32 patients (24 female, 75%) after 7.3 years average implantation (range: 1.8 to 16.1y). The components were implanted at L2/L3 (n=1), L3/L4 (n=2), L4/L5 (n=20), and L5/S1 (n=15). All the implants were removed due to intractable back pain and/or facet degeneration. In addition, they were removed due to subsidence (n=10), anterior migration (n=3), core dislocation (n=2), lateral subluxation (n=1), endplate loosening (n = 2), and osteolysis (n=1). In parallel, 7 new implants were evaluated at L4-L5 and 13 implants at L5-S1 in an in vitro lumbar spine model.

Outcome Measures
Retrieval analysis included evaluation of clinical data, dimensional measurements and assessment of the extent and severity of PE surface damage mechanisms. In vitro testing involved the observation of motion patterns during physiological loading.

Methods
For the retrievals, each side of the PE core was independently analyzed at the rim and dome for the presence of machining marks, wear, and fracture. 35 cores were further analyzed using MicroCT to determine whether the wear was one-sided, or symmetrically distributed. For the in vitro study the new implants were tested under physiologic loads (flexion-extension with a compressive follower preload) using a validated cadaveric lumbar spine model. The center of the prosthesis was 2 mm posterior to the mid-point of the vertebral body endplate in mid-sagittal plane. Motion patterns of the in vitro-tested implants were tracked using sequential video-flouroscopy.

Results
Substantial variability was observed in the wear patterns of the retrievals. 15/35 retrieved cores (43%) displayed one-sided wear patterns. The median dome penetration was 0.2 mm (range: 0.06 to 0.9 mm) and the median penetration rate was 0.04 mm/y (range: 0.01 to 0.2 mm/y). No significant difference in penetration or penetration rate was observed between retrievals with one-sided and symmetric wear patterns (p >0.05). Significant correlations were observed between implantation time and penetration (rho = 0.46, p = 0.004) and penetration rate (rho = −0.48, p = 0.003). In the in vitro study, there was clear visual evidence of motion at both articulations in 8/20 implantations. In additional 8/20 cases, there was some evidence of motion at both articulations; however, the predominant motion occurred at the top articulation. In 4/20 implantations motion could be visually detected only at the top articulation. Core entrapment and pinching was observed in 7/20 cases as the segment was extended, and was associated with visual evidence of core bending or deformation in 5/20 cases.

total disc arthroplasty, total disc replacement, lumbar spine, CHARITÉ, degenerative disc disease, artificial disc, in vitro motion response, wear, surface damage, fracture, impingement, ultra, high molecular weight polyethylene, UHMWPE

[KBear]

Very interesting, thanks for sharing this.

[Justin]

Spine. 1 August 2006 - Volume 31 - Issue 17 - pp 1900-1910

In Vitro Wear Assessment of the Charite Artificial Disc According to ASTM Recommendations
Serhan, Hassan A. PhD; Dooris, Andrew P. PhD; Parsons, Matthew L. MS; Ares, Paul J.; Gabriel, Stefan M. PhD, PE

Study Design. Biomechanical laboratory research.

Objective. To evaluate the potential for Ultra High Molecular Weight Polyethylene (UHMWPE) wear debris from the Charité Artificial Disc.

Summary of Background Data. Cases of osteolysis from artificial discs are extremely rare, but hip and knee studies demonstrate the osteolytic potential and clinical concern of UHMWPE wear debris. Standards for testing artificial discs continue to evolve, and there are few detailed reports of artificial disc wear characterizations.

Methods. Implant assemblies were tested to 10 million cycles of ±7.5° flexion-extension or ±7.5° left/right lateral bending, both with ±2° axial rotation and 900 N to 1,850 N cyclic compression. Cores were weighed, measured, and photographed. Soak and loaded soak controls were used. Wear debris was analyzed via scanning electron microscopy and particle counters.

Results. The average total wear of the implants was 0.11 and 0.13 mg per million cycles, before and after accounting for serum absorption, respectively. Total height loss was approximately 0.2 mm. Wear debris ranged from submicron to >10 μm in size.

Conclusions. Under these test conditions, the Charité Artificial Disc produced minimal wear debris. Debris size and morphology tended to be similar to other CoCr-UHMWPE joints. More testing is necessary to evaluate the implants under a spectrum of loading conditions.

© 2006 Lippincott Williams & Wilkins, Inc.


Thanks for posting these Jill!

[cavalier]

Of course one needs to keep in mind the Charite is a unconstrained device so it is more apt to have more range of motion & that may enter into the wear factor. I just know I was told for my facets due to the wear they had already Charite would put more load on my facets than the semi constrained ADR devices. So just because both have polyethylene cores & titanium endplates they are not going to necessarily wear the same due to the differences between semiconstrained and unconstrained. Although for many people the Charite has held up well so this article is not necessarily the norm either. It is just a small group they studied that had failures over time & so these would of course show the most wear it is not indicative of all.
So keep in mind those points. Best - Jill